At present, 2 million kilometers of pavement are mainly composed of traditional asphalt pavement and cement concrete pavement. Traditional pavement not only has a high bearing capacity, but also has advantages in design, materials, and structural layers. , but it also has many shortcomings, such as reducing the urban soil use area, greatly increasing the amount of sewage in the urban sewage pipe network, increasing the burden on the drainage system, etc., which accelerates the application of permeable concrete in road construction .
Introduction to permeable concrete
Permeable concrete is also called porous concrete. It uses single-grain coarse aggregate as the skeleton and is wrapped in a thin layer of cement slurry or mortar with a small amount of fine aggregate. On the surface of coarse aggregate particles, as a cementing layer between aggregate particles, a skeleton is formed - a porous concrete material with a pore structure. Due to the special gradation of the aggregates, a honeycomb structure is formed, or is called a popcorn candy structure. It has both a certain strength and a certain degree of water permeability and breathability. From the perspective of technical performance, permeable concrete can not only quickly reduce surface water accumulation, but also has obvious effects in purifying rainwater and reducing road traffic noise.
Analysis of the advantages and disadvantages of permeable concrete compared with traditional pavement
Traditional pavement
Most of them are laid with asphalt, cement concrete, stone slabs or cement bricks, so they are called For hard roads. The overall advantages of traditional pavement are high bearing capacity, neat, smooth and durable surface layer. The disadvantages of traditional pavement are: (1) It is impermeable and requires underground sewage pipes for drainage. When it rains, rainwater is directly treated as sewage, which blocks the replenishment of groundwater by rainwater and is not conducive to the generation of groundwater. (2) Rainwater and sewage easily accumulate on the road surface and dissolve into urban pollutants, seriously affecting urban sanitation.
Permeable concrete pavement
Compared with traditional concrete pavement, permeable concrete pavement has the following advantages. (1) High water permeability. The permeable concrete floor has 15% to 25% pores. The water permeability rate of the concrete surface layer can reach more than 200L/m2/min, which is much higher than the discharge rate of the largest rainfall under the best drainage system. ; It can quickly penetrate rainwater into the ground and restore it to groundwater, so that groundwater resources can be replenished in a timely manner [3]. (2) Permeable concrete has a large porosity, which increases the urban water and air permeability area, strengthens the heat exchange between the water inside the concrete and the ground surface and the air, and is conducive to regulating the city by connecting with the outside air and the lower permeable cushion. Humidity and temperature of the space. (3) Permeable concrete pavement, with its unique 15% to 25% porous structure, not only absorbs dust, but also absorbs the noise generated when vehicles are driving, thereby creating a quiet and comfortable environment. (4) Permeable concrete pavement can reduce the phenomena of "slipping" and "splashing" caused by driving on rainy days, and alleviates the inconvenience caused to pedestrians and vehicles on rainy days. (5) The natural color of the permeable concrete pavement surface has good reflectivity to light. The larger pores of permeable concrete can accumulate more heat, which is beneficial to reducing the absorption of solar heat by the road surface, thus avoiding the formation of the "heat island effect". (6) During the snowfall season, geothermal heat can melt the accumulated solid snow into liquid water through the pores of the permeable concrete pavement, and then penetrate into the ground to replenish groundwater. Although permeable concrete pavement has many of the above advantages, it also has the following disadvantages. (1) The drainage function is not maintained for a long time, and usually good drainage function only lasts for 1 to 2 years; (2) Due to large pores, it is susceptible to oxidation of harmful substances in the air and damage by ultraviolet rays, and its service life is short. (3) When using high-viscosity materials and asphalt as base materials, although their strength and thermal stability are increased, the cost is too high. In view of the above reasons, these issues need to be taken into consideration in the widespread promotion and application of urban construction.
Introduction to key construction technologies of permeable concrete
Controlling the paving, compaction and curing quality of the concrete surface layer is the key to permeable concrete construction technology.
Paving
When paving, the lateral spacing of the reference line is the paving width of the surface layer plus the lateral spacing, in which the distance from the reference line to the edge of the surface layer paving should be the same; datum The longitudinal spacing between line piles: the straight section shall not be greater than 10m, and the curved section shall not be greater than 5m; the baseline must be tightened, and the line pressure shall not be less than 1000N.
The formwork should be made of materials with good strength, no deformation, and high rigidity; the height of the formwork should be consistent with the thickness of the concrete, and the surface in contact between the formwork and the concrete should be coated with release agent, and the concrete mixture should be spread evenly and flat manually; Expose the drainage slope under the road surface and connect the blind ditch with the urban drainage system; ensure the thickness of the permeable concrete pavement, especially the even spreading, pay attention to edge and corner defects, and use manual compaction.
Compaction
Use special tools such as low-frequency vibrating rollers or flat rollers. The vibrator plate should avoid continuous vibration in one place to avoid segregation or over-vibration. During the compaction process, manual leveling should be supplemented. If there is a lack of material in the surface layer, sinking, deformation or looseness, manual shoveling should be used to correct it in a timely manner. When compacting the permeable concrete surface layer, if the surface cannot be reached by machinery, manual compaction must be used. The top of the formwork used must be clean and smooth, and the joints must be poured with concrete. Construction cannot be performed on rainy days. The construction time interval between the upper and lower layers should not exceed 1 hour.
Maintenance and joint cutting
After the permeable concrete pavement is paved and compacted, in order to avoid cracks on the pavement and extend the service life of the road, the pavement must be properly maintained. , such as during high-temperature construction, in order to avoid excessive moisture loss, the road surface must be maintained by covering it with plastic film, and the concrete surface layer must be properly sprinkled and maintained. In addition, it is necessary to master the cutting time of the road surface. If the cutting time is too early, the road surface layer will not be strong enough and it will easily cause edge collapse. If the cutting time is too late, the road surface layer will shrink due to excessive shrinkage and cracks will occur. Secondly, the pavement cannot be opened to traffic during the maintenance period. Traffic must be released after the concrete has sufficient strength to ensure the quality and service life of the permeable concrete pavement.
The use of permeable concrete pavement allows rainwater to quickly penetrate into the ground without causing hypoxia. This design will not have a negative impact on plants. Traditional concrete pavements are not permeable, allowing rainwater to flow into the urban drainage system. When the sewage flow in the drainage system exceeds the processing capacity of the sewage treatment facilities, it will be directly discharged into public waters, causing water pollution. Permeable concrete pavement will be widely promoted and developed in urban road construction.
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